The Lantern pleads guilty: The keys to living a more environmentally friendly life aren't universal, and the greenest choices for your home and community often vary across the country. For a good example, it's worth looking at a recent Yale study (subscription required) on the great debate over mercury in compact fluorescent light bulbs.

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A quick refresher: CFLs have become the eco-conscious bulb of choice, on account of their longer lifespan and reduced energy use. (By federal law, the fluorescent bulbs will entirely replace incandescents on store shelves by 2014.) Skeptics have cried foul, calling attention to the fact that a small amount of mercury is used in manufacturing the bulbs. Yet, as the Lantern and others have pointed out, electric power that comes from coal—like nearly half of electricity generated in the United States—is responsible for its own mercury emissions. So overall, using CFLs actually reduces the amount of mercury pollution.

According to the Yale paper, the truth is slightly more complicated. In most states—42, to be exact—switching to CFLs does appear to result in a net reduction of mercury emissions. But that's not true in Alaska, California, Idaho, Maine, New Hampshire, Oregon, Rhode Island, and Vermont: In these states, mercury emissions would actually increase if everyone started using CFLs.

Why is that? The biggest factor is how those states generate their electricity. By and large, the eight outliers are far less reliant on coal than the rest of the country. (Here, Vermont and Rhode Island take the cake—they don't have any coal-fired power plants at all.) * Mercury emissions also depend on what kind of coal a state uses and on the pollution controls installed at each power plant.

That means that in some states, at least, there's a real (albeit small) tradeoff involved in switching to CFLs. The Lantern still thinks CFLs are a good choice, even if you live in Vermont. For one, overall mercury emissions are likely to be lower to begin with, simply because of the lower reliance on coal-fired power plants. (Indeed, the magnitude of mercury reductions from making the switch in coal-heavy states like West Virginia would be far larger, per bulb, than the corresponding increase in a state like Vermont.) And from an individual perspective, it's easy enough to ensure that CFLs don't result in added mercury emissions wherever you happen to live: As long as you recycle them properly, the mercury won't pose too much of a problem. (Home Depot, Ikea, and True Value, among other retailers, will take your old CFLs; the EPA can help you find other recyclers here.)

Let's get back to your original question. The same issue of local energy sources applies to how you heat your home. The Lantern usually suggests heating your house with natural gas rather than electricity, because natural gas produces fewer carbon emissions per unit of heat than does coal. But if you live in Vermont, electricity produces relatively little carbon, so natural gas—which is, after all, a fossil fuel that is often environmentally costly to extract—doesn't look quite so good.

When it comes to living green, it's always a good idea to know where your electricity comes from. (Fortunately, this handy search tool from the EPA can help.) If your power company uses more coal than the national average, then be extra careful to cut down on your electricity use. And if it uses much less, then electricity might not be quite as bad as other fossil fuel sources.

The same idea holds true for water usage. Wasting water is always somewhat problematic, since sending lots of tap water down the drain puts more strain on the water-treatment system. But in some parts of the country—easily identified on this map—drought is a major concern.

If you are unsure, the best thing to do is ask. Every state has agencies tasked with protecting the local environment, and the folks who work at these departments should be able to answer questions about your own community. Even when you're talking about global warming, some of the best information is still local.

Is there an environmental quandary that's been keeping you up at night? Send it to ask.the.lantern@gmail.com, and check this space every Tuesday.

* Correction, Jan. 15, 2009: The original story incorrectly stated that Vermont and Rhode Island don't use any coal. The two states do not have any coal-fired power plants but receive some electricity that may come from coalfrom other states.(Return to the corrected sentence.)